As semiconductor devices have been becoming finer in recent years, various material films having different properties are formed on a substrate, which is processed to provide the semiconductor devices. In particular, in a damascene interconnect forming process for forming interconnects by filling a metal into interconnect trenches formed in the substrate, an excessive metal is polished away by a substrate polishing apparatus after the damascene interconnect forming process is performed. Various films, such as a metal film, a barrier film, and a dielectric film, having different wettabilities with respect to water, are exposed on the substrate surface that has been polished. Residues, such as slurry used in polishing and polishing debris, remain on these films that are exposed on the substrate surface. In order to remove these residues, the polished substrate is transported to a substrate cleaning and drying apparatus, where the substrate surface is cleaned and dried (See Japanese laid-open patent publication No. 2009-117794 and Japanese patent publication No. 3556043).
However, if the cleaning of the substrate surface is insufficient, reliability problems, such as poor adhesion and a current leak at a portion to which the residues are attached, may occur. Therefore, in manufacturing of the semiconductor device, the cleaning and drying of the substrate have been becoming an important process for improving a product yield.
FIG. 16 shows a schematic cross-sectional view of an example of a substrate cleaning and drying apparatus. This substrate cleaning and drying apparatus includes a substrate holder 301 for holding a substrate W, a motor 302 for rotating the substrate holder 301, a cylindrical cup 303 disposed around the substrate W, and a cleaning liquid supply nozzle 304 for supplying a cleaning liquid, such as pure water or a chemical liquid, onto the surface of the substrate W. The substrate holder 301 includes a substrate stage 311 coupled to the motor 302 through a support shaft 312. A plurality of chucks 310 for gripping a peripheral portion of the substrate W are provided on the substrate stage 311.
When the substrate W is cleaned, the cleaning liquid is supplied onto the surface of the substrate W while the substrate W is rotated by the motor 302 at a relatively low speed (for example, about 300 to 600 min−1). When the substrate W is dried, the substrate W is rotated at a relatively high speed (for example, about 1000 to 2000 min−1) so as to spin off the cleaning liquid from the surface of the substrate W. The cleaning liquid, spun off from the substrate W, is caught by the cylindrical cup 303 and is then recovered or discarded.
As shown in FIG. 16, the cylindrical cup 303 is typically disposed around the substrate W that is rotated by the motor 302. The cylindrical cup 303 has an inner circumferential surface that receives the liquid scattered around by the rotation of the substrate W. The cylindrical cup 303 can thus prevent the liquid from being scattered, and can downsize the apparatus in its entirety. A liquid pan 363 is provided at the bottom of the cylindrical cup 303, and exhaust ports 315 are formed in this liquid pan 363. The exhaust ports 315 are coupled to a suction device (not shown), such as a vacuum pump, so that air in the cylindrical cup 303 is exhausted together with the cleaning liquid through the exhaust ports 315.
However, it is difficult to make a uniform exhaust environment around the rotating substrate W in the substrate cleaning and drying apparatus having the above-described constitution. More specifically, a velocity of an exhaust flow is high in a region close to the exhaust port 315, while a velocity of an exhaust flow is low in a region distant from the exhaust port 315. A schematic view of such exhaust flow is shown in FIG. 17. FIG. 17 is a schematic view illustrating the velocity of the exhaust flow in the case where the inside of the cylindrical cup 303 is exhausted through one exhaust port 315 provided in the bottom of the liquid pan 363. In FIG. 17, the flow velocity is indicated by size of arrow. When only one exhaust port 315 is provided as shown in FIG. 17, uniform exhaust flow having an equal velocity cannot be formed around the substrate W. Furthermore, since the substrate W is rotated together with the substrate stage 311, the air flow in the cylindrical cup 303 is stirred, and as a result an upward flow may be generated between the substrate W and the cylindrical cup 303.
When the substrate W is rotated, if the velocity of the exhaust flow around the substrate is not uniform, or in particular if the upward flow is generated on the peripheral portion of the substrate W, mist and droplets of the cleaning liquid (e.g., pure water) that has been once removed from the substrate W may be carried onto the substrate W. The mist and the droplets of the cleaning liquid, attached again to the substrate W, may produce water-marks on the surface of the substrate W. The water-marks adversely affect devices formed on the substrate W, thus reducing a product yield. Moreover, the cleaning liquid that has been attached again may cause a back contamination of the substrate W. Furthermore, when the substrate W is dried by the rotation of the substrate, if the velocity of the exhaust flow around the substrate is not uniform, the peripheral portion of the substrate W is not dried uniformly. Therefore, it is an important issue for the substrate cleaning and drying apparatus to make the exhaust environment uniform around the substrate.
In order to solve the above-described issue, the following construction is proposed. Plural exhaust holes 315a whose diameters become gradually larger in accordance with a distance from the exhaust port 315 are provided around the peripheral portion of the substrate so that air that has passed through these exhaust holes 315a is exhausted through the exhaust port 315. FIG. 18 shows a schematic view showing the exhaust flow according to this structure. In FIG. 18, the flow velocity is indicated by size of arrow. The construction shown in FIG. 18 can improve the uniformity of the exhaust environment to some extent, compared with the construction shown in FIG. 17. However, it is difficult to make the velocity of the exhaust flow completely uniform around the substrate W.